Is Spray Foam Insulation Waterproof? Open cell foam is not waterproof or water-resistant. In contrast, closed cell foam is water-resistant. However, only high-density closed cell foams are waterproof.Click to see full answer. In this manner, is expanding foam sealant waterproof?Fill and seal expanding foam sealant is urethane foam designed to fill large areas quickly and permanently. Uses include filling holes, cracks or gaps that require a complete airtight and waterproof seal but are too large to be filled with ordinary caulk. can spray foam be used outside? Using Spray Foam Insulation In Exterior Walls. Spray foam insulation is a very popular way of keeping the interior of homes warm during the coldest parts of the year. Spray foam is well known for it’s ease of use and installation within a variety of exterior walls surfaces. Also to know is, can mold grow on spray foam insulation? As a product, spray foam insulation does not attract mold. And unlike wood or metal, spray foam does not rot, rust or deteriorate. This means that an area properly sprayed with foam insulation will never become a food source or a hospitable environment for a mold colony.Does foam insulation absorb water?Closed cell foam insulation normally does not absorb water and under most situations will not have to be removed.